Cathode spreader for flat cathodes



Nov. 26, 1957 w. R. CHEATLE CATHODE SPREADER FOR FLAT cm-xonns Filed July 10, 1953 INVEN1I'OR WILFRED R. CHEATLE ma/w ATTORNEY I 2,814,090 Patented Nov. 26, 1957 fiice CATHODE SPREADER FOR FLAT CATHODES Wilfred R. Cheatle, Emporium, Pa., assiguor to Sylvania Electric Products Inc., a corporation of Massachusetts Application July 10, 1953, Serial No. 367,261

9 Claims. (Cl. 29-2516) This invention relates to an improvement of the method of manufacture of electron tubes and to tools for carrying out the method.

In order to obtain certain characteristics in a tube, it is sometimes necessary to have the distance between electrodes very small. In the case of a grid controlled tube having a high mutual conductance or Gm, the distance between control grid and cathode should be made very small. In assembling such tubes where adjacent electrodes are of the final desired dimensions, one electrode is apt to rub against the other with possible injury to the electrodes or their coatings.

It is an object of this invention to provide a method so that there is much less likelihood of injury to the tube components during assembly than heretofore, While yet providing for a simple method of finally forming the assembled parts to obtain desired positional relationships of the parts.

It is a further object of my invention to provide a simple tool for carrying out my method.

For a better understanding of my invention, attention is directed to the following specification and claims and the accompanying drawings in which:

Fig. 1 is a perspective view of a typical mount of a tube having a high transconductance, parts being broken away to expose salient portions of the mount, and with the cathode bowing exaggerated to better illustrate the construction of the type of tube here involved.

Fig. 2 is a diagrammatic plan view of the triode portion of the mount.

Fig. 3 is a diagrammatic plan view of the cathode, grid and a fragment of a support wafer prior to spreading of the cathode, the opening in the wafer for reception of the cathode being exaggerated as to minor axis diameter.

Fig. 4 is a view similar to Fig. 3 but with the cathode spread, the figure also showing, in section, the tool utilized in the process.

Fig. 5 is a view of one form of a tool employed in the process, showing the proportion of parts.

Fig. 6 is a very much enlarged perspective view of one form of tool utilizable in the manufature of the mount, the handle being broken away.

Fig. 7 is a section through the tool at its spreader portion, taken along the line 77 of Fig. 6.

Fig. 8 is a view similar to Fig. 6 showing a modified form of tool.

Referring to Fig. 1 there is shown a vacuum tube mount 10 with cathode 12, grid 14 and anode 16. For exemplification, the tube disclosed is a 61 4WA type which requires exceedingly close cathode and grid. This type of tube has an anode which is comprised of two spaced bent plates 18, reinforced by braces 22. The cathode is suitably held between a pair of insulating wafers 24, and the grid is supported by grid side rods 26, which may be deformed, if desired, after insertion of the rods into the wafers to firmly hold the grid in place. The anode plates have twisted or bent lugs 28 projecting through the Wafers to hold the plates in place. The

braces 22 are spot welded or otherwise suitably secured to the anode plates.

The relationship of the various parts and the closeness of electrodes can be seen by considering the diagrammatic representation in Fig. 2, of the just described components.

The insulating wafers may have openings to receive the cathodes which before assembly are of rectangular unbowed form and these openings have the rectangular form and outside diameter of the unspread cathode or they may have openings in which the long sides of the rectangle are bowed outwardly very slightly. An exaggerated bow in the wafer 24 is shown in Fig. 3 at 30.

In assembling the mount, the bottom wafer has first assembled on it the cathode 12 in its parallelepipedon form and the anode assembly 16. Then the grid structure 12 is slipped over the cathode and mounted on the lower wafer, and the top insulating wafer, provided with openings similar to the bottom wafer, is applied to the mount. The lugs 28 are then bent and the rods 26 deformed, if desired, above and below the wafers to fix the grid in place. In the case of manufacture of diodes, the anodes might be mounted very close to the cathode so that were an attempt made to mount parts to occupy their final positions, damage to the electrodes, particularly to the coating on the cathode, may well take place. Therefore, even in the assembly of a diode mount, it is desirable to follow the teaching of this inventor. Following such teaching, the cathode to be mounted should be of a cross section, not necessarily rectangular, such that it may be spread to bring parts of it closer to the anode or anodes.

To complete the mount assembly, a cathode spreading tool, about to be described, is inserted into the cathode along the axial center of the cathode and is rotated to slightly distend the large area faces of the cathode. In the process, because the distention is slight, no damage is done to the cathode coating; the insulating wafer, if provided with a rectangular opening, will yield the slight amount necessary. Where the wafers have bowed wall openings, the distention of the cathode may be more freely accomplished without injury to the wafers. It has been found in practice, that by following the teachings of this invention, the losses in manufacture are far below those where the assembly is effected with prebowed cathodes. In the priorart method damage to the cathode coating or distortion of other electrodes is a quite frequent occurrence resulting in considerable tube losses or shrinkage. The tool 32 utilized tobow the cathode, in one form of my invention, is shown in Fig. 5, and in enlarged fragmentary perspective in Fig. 6. -It comprises a socketed handle 34 and aneedle 36 secured in the handle by any convenient means such as a set screw 38 threaded into the handle and engaging the needle portion lying in the socket of the handle. The needle 36 itself is comprised of a cylindrical portion 40 and a second spreader portion 42 of reduced diameter with respect to the cylindrical portion to provide a shoulder 44 for a purpose to be described. The free end of the needle may be tapered as shown at 45.

The spreader has two parallel fiat sides spaced apart a distance barely under the minor diameter of the unspread cathode and two opposed rounded surfaces 48 whose maximum spacing is equal to the desired final distended internal minor dimension of the cathode. The handle 34 has a fiat portion 50 parallel to the fiat face 46 of the spreader to indicate, to the operator by feel, the angular position of the spreader flat faces. Instead of the needle being mounted in a socketed handle, it may obviously project upwardly from a flat base resting on a suitable support such as a table.

In use, after the parts of the tube have been mounted as described above, the spreader is inserted into the cathode at about its medial longitudinal axis and thrust in until the shoulder 44 engages the edge of the cathode. Then the tool and cathode are relatively rotated 180 or more, thus causing the rounded edges of the needle to engage the cathode walls to be bowed. Since the maximum distance between the rounded ends of the tool is greater than the distance between the walls to be bowed, there will be effected a spreading of the cathode to bring the outer face of the cathode closer to the grid. After the cathode has been spread, the tool is retracted. The mount then is further processed, as is usual in the art.

If desired, particularly where wafers with rectangular openings for the cathode are provided and in order to prevent possibility of breakage of the wafer about the cathode when the cathode is enlarged, the form of spreading tool shown in Fig. 8 may be employed.

This tool differs from the tool previously described in that not only the free end 52 of the spreader, but also the end 54 adjacent to the shoulder 56 have their rounded cylindrical sides approach each other very slightly. Thereby neck portions are formed at both ends of the needle. As a result, when the tool is inserted in a rectangular cathode and rotated, the cathode will spread between the wafers; at the level of the wafers, the spread will be exceedingly little, if at all, thus reducing any tendency for the wafer to crack or crumble. Where the wafers are provided with rectangular holes, the cathode is slightly bulged between the wafers and held against excessive longitudinal movement with respect to the wafers when parts are cold. The length of the operative surfaces of the needle is proportioned to the length of cathode between wafers to secure this result.

The tool itself is claimed in divisional application Serial No. 621,695, filed November 13, 1956.

Having thus described my invention, which I claim as new is:

1. In the process of manufacture of radio tubes, the steps of mounting a hollow cathode and a surrounding grid between insulating wafers and spreading walls of the so-mounted cathode to cause them to approach the grid.

2. In the process of manufacture of radio tubes, the steps of mounting a tubular cathode, rectangular in cross section, and a surrounding grid between insulating wafers, and bowing those walls of the cathode toward the grid which include the longer sides of the rectangle.

3. In the process of manufacture of radio tubes having tubular cathodes and grids surrounding the cathodes,

the grids having bowed sections, the steps of mounting a r hollow cathode, rectangular in cross section, and a bowed grid between a pair of insulating wafers and subsequently deforming walls of the cathode toward the bowed sections of the grid.

4. In the process of manufacture of radio tubes, the steps of mounting a cathode on an insulating wafer, slipping a grid over the cathode and mounting the same on the wafer, mounting an anode structure on the wafer, applying a second wafer on to the assembled parts, and then spreading the cathode to cause outer walls thereof to approach the grid.

5. In the process of manufacture of radio tubes, the steps of mounting a tubular cathode, rectangular in cross section, and a surrounding grid between insulating wafers, and spreading walls of the so-mounted cathode toward the grid by forces applied to the mid portions of the cathode walls within which lie the longer sides of the rectangle, the force applied being along an axis parallel to the longitudinal axis of the cathode.

6. In the process of manufacture of radio tubes having tubular cathodes and grids surrounding the cathode, the grids having bowed sections, the steps of mounting a hollow rectangular cathode and said bowed grid between a pair of insulating wafers and subsequently forcing walls of the cathode including the longer sides of the rectangle toward the bowed sections of the grid by forces applied to the mid portion of said walls along an axis parallel to the longitudinal axis of the cathode.

7. In the process of manufacture of radio tubes, the steps of mounting a cathode, rectangular in cross section, on an insulating wafer, slipping a grid over the cathode and mounting the same on the wafer, mounting an anode structure on the wafer, applying a second wafer onto the assembled parts, and then spreading the cathode to cause outer walls thereof within which lie the longer sides of the rectangle to approach the grid, by forces applied to the mid portions of said walls along an axis parallel to the longitudinal axis of the cathode.

8. In the process of manufacture of radio tubes in which there is a substantially rectangular in cross section cathode with slightly bowed walls close to an encompassing grid, the steps of assembling parts including a cathode, rectangular in cross section, and a surrounding grid between a pair of insulating wafers, applying forces internally of the cathode along the length of the cathode with a component of force at right angles to the long axis of the rectangle, to effect spreading of cathode walls.

9. In the manufacture of a radio tube mount having an insulating wafer, the steps of mounting a hollow electrode and a cooperating electrode on the wafer, and spreading the so mounted hollow electrode to cause portions thereof to approach the cooperating electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,578,462 Myers Mar. 30, 1926 1,620,920 Porter Mar. 15, 1927 2,000,163 Clark May 7, 1935 2,024,585 Laico Dec. 17, 1935 2,174,853 Bowie Oct. 3, 1939 2,518,273 Bergstrom Aug. 8, 1950 2,573,327 Gossard Oct. 30, 1951 

